It’s known that one form of the neurological disorder that strikes early in life is linked to a genetic mutation that makes some people prone to the disease.

But the new research suggests the risk of developing Parkinson’s later in life – which is far more common – is also controlled by genes.

A team at the National University Hospital in Iceland studied 772 people who developed Parkinson’s after age 50.

And they found the risk of Parkinson’s was 6.7 times higher among people who had a brother or sister with the disease.

The risk was 3.2 times greater among people who had a parent who had developed Parkinson’s.

The researchers said the effects of the genetic mutation are subtle – which is why Parkinson’s often skips generations.

They also found no evidence that spouses were more likely to develop Parkinson’s. This suggests that environmental factors, such as exposure to chemicals later in life, do not play a role.

But the researchers left open the possibility that environmental factors shared by family members early in life could be a factor.

“This may indicate a role for some shared environmental factor early in life,” the team writes in the New England Journal of Medicine.

A spokeswoman for the Parkinson’s Disease Society told the BBC in Britain:

“Most people now believe that, as with many other common conditions, Parkinson’s is likely to have a genetic component. [This] makes some individuals susceptible to something in the environment, perhaps a chemical or a virus.”